Ex vivo 3H-spiroperidol binding to rat striatum and the inhibitory effects of neuroleptics.

Abstract

Abstract-Neuroleptic drugs were given to rats and at different time intervals the animals were decapitated and 3H-spiroperidol binding to the striatal homogenates was determined in vitro. Two hours after an intraperitoneal administration of spiroperidol, perphenazine, haloperidol, chlorpromazine or thioridazine in doses of 0.03-30 mg/kg, 3H-spiroperidol binding to the striatal homogenates was inhibited dose-dependently with an ID50 value of 0.11, 0.23, 1.1, 3.7 or 9.4 mg/kg, respectively. After a single intra muscular administration of fluphenazine enanthate (10 mg/kg), a long acting neuroleptic drug, long-lasting inhibitory effect (over 4 weeks) on the binding was also observed. These results indicate that ex vivo 3H spiroperidol binding method may be useful to measure the duration and the potency of anti-dopaminergic activities of drugs. receptors, and phar macokinetic characteristics can be elucidated. The present study was carried out to demon strate the validity of the ex vivo 3H spiroperidol binding method. MATERIALS AND METHODS Pilot experimentsto select the tissue preparation and the optimun ligand concen tration for ex vivo study: Male Sprague Dawley rats (180-250 g) were given saline or 3 mg/kg chlorpromazine (CPZ i.p.). Two hr later, the rats were decapitated and the striata homogenized in 35 volumes of ice-cold water. Aliquots (3 ml) of the striatal homogenates were further centrifuged at 20,000xg for 20 min at 40, and the pellets resuspended in 3 ml of ice-cold water. To assess the degree of CPZ incorporation among these fractions, striatal homogenates (0.5 ml, obtained from rat treated with CPZ), membrane fraction (0.5 ml, CPZ) or supernatant fraction (0.5 ml, CPZ) plus membrane fraction (0.5 ml, control) were incubated for 15 min at 370 with 62.5 pM 3H-spiroperidol , according to the method of Fields et al. (2) with slight modification. In the kinetic study, high affinity 3H spiroperidol binding to striatal homogenates was determined at five different ligand concentrations -0.031, 0.0625, 0.125, 0.25 and 0.5 nM. The incubation mixture (in triplicate) with a total volume of 10 ml